Transferring posts between communities is a lot more... complex... than you'd think.
Firstly, unless there's migration paths opened already (which there are not for the 'community' to use to move things to / from Ask UbuntU), migration of questions between communities requires the moderators on the origin site to intervene to moderate.
Secondly, the older ...
There are several options.
Perhaps the easiest is to use separate code fences like this:
Which produces this:
Another way is to insert a line rule by putting three (or more) hyphens/dashes (---) on an empty line, without indentation, between the blocks, which produces a sharper separation:
I'll post an answer since it's hard to do in comments. I will be using this review item as an example: https://askubuntu.com/review/low-quality-posts/1123857
Now, on to your specific points.
identify post: the banner at the top shows very prominently infos about the question (which is totally irrelevant when reviewing an answer)
I honestly don't ...
What's going on is described here on Meta Stack Exchange: Visual design changes to the review queues. That is also the place to leave feedback. They've already improved quite a lot of things reported by the community in the first round (Close/Reopen review queues on Meta Stack Exchange/Meta Stack Overflow) so perhaps they will take your criticism as well, as ...
Ask Ubuntu has a built-in image uploader:
If you use it with less than 10 reputation, it will add them as links to your post; this is to prevent abuse. However, you can hope another user will convert them to properly inlined images.
If you are using Ubuntu or one of the other official flavors, you can ask your question on Ask Ubuntu, although you can also ask it on Unix & Linux - your choice. I would suggest looking for questions similar to the one you want to ask on both sites to reach a decision as to where you're most likely to get the kind of answers you want.
If you are using a ...
That's the one you're looking for; then, choose "A community-specific reason" and you'll get the familiar list of options:
They have renamed the option last year; for details, see Question Close Updates: Phase 1 on Meta Stack Overflow.
The Help Center explains that answers that do not provide an answer to the original question will be deleted. The structure of this site doesn't support posting a comment on another post as an answer, because the general idea is to make it as easy as possible to find the best answer to the question. So:
Posts that don't answer the question would be "...
There is a slight downside, and that's existing comments containing a @yourname or yourname will become outdated and potentially confusing, especially if the display name is similar/duplicates someone else's.
I've seen replies in comments addressed to a user who since renamed themselves.
Just because the questions haven't been closed doesn't mean they're on topic. The specific policy is:
Any non-official variant or flavor of Ubuntu such as Regolith, Mint, PopOS, etc. are considered offtopic here on Ask Ubuntu.
To quote the Help Center (links stripped by me)
Questions that you may ask:
Using and administering official Ubuntu flavors: ...